Multilayer film

ABSTRACT

A flexible multilayer film suitable as a (food-)packaging material includes a first seal layer comprising principally a metallocene-catalyzed polyolefin, and a second seal layer comprising a copolymer of at least one oxygen-containing monomer and ethylene. The copolymer is set to have a crystal melting point lower than that of the metallocene-catalyzed polyolefin. The second seal layer may preferably have a thickness larger than that of the first seal layer. Because of the provision of the second seal layer adjacent to the first seal layer, the multilayer film is provided with an improved film-formability while retaining the good sealability of the metallocene-catalyzed polyolefin.

This is a divisional of Ser. No. 08/688,878, filed Jul. 31, 1996, U.S.Pat. No. 6,063,462.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a multilayer film including a sealstructure comprising a seal layer and a second seal layer, morespecifically a multilayer film including a seal layer comprisingprincipally a polyolefin produced by polymerization in the presence of ametallocene catalyst (hereinafter termed a “metallocene-catalyzedpolyolefin”), which is excellent in film-formability, sealability andflexibility.

A metallocene-catalyzed polyolefin is generally excellent insealability, hot tack and transparency but is liable to be accompaniedwith poor film-formability or film-processability. Moreover, whiledepending on the shape or form of a package, a flexible multilayer filmformed therefrom is liable to have insufficient sealability, filmstrength and heat resistance.

Several packaging materials using metallocene-catalyzed polyolefins havebeen proposed. For example, Japanese Laid-Open Patent Application (JP-A)6-8383 (Bekele) discloses a cook-in film having an improved sealstrength, including: a seal layer comprising a polyamide blend, and acore layer and an outer layer each comprising a metallocene-catalyzedethylene-butene copolymer, of which at least the seal layer iscrosslinked. JP-A 7-1680 (Bekele) discloses a multilayer film showing alow oxygen permeability, including at least one oxygen-barrier layercomprising a blend of a terpolymer of monomers selected from ethylene,an acrylic acid ester, maleic acid and glycidyl methacrylate, and anethylene-vinyl alcohol copolymer, and also a surface layer comprising ablend of metallocene-catalyzed polyolefin on a non-sealing side. JP-A59-143639 (Oval) discloses a six-layered shrinkable film including afirst layer (seal layer) of, e.g., propylene-ethylene random copolymeror ionomer resin having a higher softening point than a second layer(shrink layer) which has a thickness large enough to govern a shrinkingtemperature of the entire multilayer film by the shrinking temperatureof the second layer and comprises, e.g., ethylene-vinyl acetatecopolymer or linear low-density polyethylene of identical thickness, athird layer (adhesive layer) of modified polyethylene, a fourth layer(gas impermeable layer) of hydrolyzed ethylene-vinyl acetate copolymer,a fifth layer (adhesive layer) and a sixth layer (abrasion-resistantlayer). JP-A 6-210810 (Lamesh) discloses a back-seamable multilayerfilm, which is a heat-shrinkable multilayer film including aheat-sealing layer comprising a blend of at least ca. 50wt. % of apropylene-based copolymer and a homogeneous ethylene-α-olefin copolymerhaving a density of below ca. 0.90 g/cc. JP-A 6-320685 (Ohmori et al)discloses a polyolefin-based multilayer film having a gas-barrier layer,and polyolefin resin layers including innermost and outermost layerseach comprising an ethylene-type copolymer having a molecular weightdispersion factor (weight-average/number-average molecular weight ratio)of below 3 and an intermediate layer of ethylene-methacrylic acidcopolymer. The multilayer film may be irradiated with electron rays fromthe surface layer. JP-A 6-166157 (Yoshii) discloses a multi-layer blownplastic container including a gas barrier layer and a layer ofmetallocene-catalyzed polyolefin resin having a molecular weightdistribution factor of below 2.5.

As described above, a metallocene-catalyzed polyolefin has advantageousproperties including excellent sealability, hot tack and transparencybut is also accompanied with a difficulty of poor film formability. Amajor characteristic of a metallocene-catalyzed polyolefin is that ithas low melt tension. Further, because of a narrow molecular weightdistribution, a sufficient degree of molecular entanglement does notoccur in a melting state, so that the metallocene-catalyzed polyolefinis liable to cause melt fracture during film forming or film processingto result in poor film surface properties and cause difficulties, suchas unstable bubble formation in the inflation process and low drawresonance, whereby stable film forming or film processing becomesdifficult. Regarding the sealability, a metallocene-catalyzed polyolefincan provide a large seal strength when formed in an ideal seal shape butgenerally shows a narrow seal condition or range, so that it is liableto cause a flow at a seal line and result in a lower strength because ofa smaller thickness. The above difficulties may be alleviated to someextent, e.g., by introducing longchain branches onto a main chain of themetallocene-catalyzed polyolefin, but it is not sufficient in somecases.

As described above, it is difficult to obtain a flexible multilayer filmexcellent in film formability and sealability only by disposing a seallayer of a metallocene-catalyzed polyolefin, and further improvement isdesired.

SUMMARY OF THE INVENTION

Accordingly, a principal object of the present invention is to provide aflexible multilayer film excellent in film formability or filmprocessability and sealability.

According to the present invention, there his provided a multilayerfilm, including: a first seal layer comprising principally ametallocene-catalyzed polyolefin, and a second seal layer comprising acopolymer of at least one oxygen-containing monomer and ethylene; saidcopolymer having a crystal melting point lower than that of themetallocene-catalyzed polyolefin.

It is preferred that second seal layer has a thickness larger than thatof the first seal layer. In case where any of the first seal layer andthe second seal layer comprises a mixture of polymers, theabove-mentioned crystal melting point relationship should be satisfiedbetween the polymer species occupying the largest proportions in thefirst seal layer and the second seal layer respectively. The multilayerfilm may preferably have a secant modulus at 2.5% strain of 150-450 MPaas a whole.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

A metallocene catalyst used in production of the metallocene-catalyzedpolyolefin in the present invention refers to a catalyst comprising acompound having a structure wherein a transition metal is sandwichedwith a pair of unsaturated cyclic compounds, which may have variousforms based on different species of metals and ligands, and may be usedas polymerization catalysts for olefins, such as ethylene and propylene,and other vinyl monomers, such as styrene, in combination with specificpromoters as desired. The metallocene catalysts are also called Kaminskycatalysts, Kaminsky-Sinn catalysts, single-site catalysts, orhomogeneous catalysts.

A constrained geometry catalyst is a type of metallocene catalystdeveloped by Dow Chemical Company. The constrained geometry catalyst mayprovide ethylene-α-olefin copolymers which may be classified as asubstantially linear polyethylene resin having ca. 0.01-ca. 3,preferably ca. 0.1-ca. 1, more preferably ca. 0.05-ca. 1, long-chainbranch(es) per 1000 carbon atoms. Because of long-chain branches eachhaving ca. 6 or more carbon atoms selectively introduced into itsmolecular structure, the ethylene-α-olefin copolymer may be providedwith excellent physical properties and good formability orprocessability, and an example thereof is commercially available fromDow Chemical Company under a trade name of “Affinity” (including1-octene as α-olefin).

A characteristic of the metallocene catalyst is the homogeneity ofactive sites, thus resulting in a product polymer having enhancedhomogeneity of molecular weight, molecular weight distribution,composition and compositional distribution. For example, a largercomonomer content provides a lower density, a lower melting point, and afilm having improved strength and transparency but also lowerheat-resistance and film processability. The metallocene-catalyzedpolyolefin can contain comonomer units introduced uniformly into themain chain and is relatively free from a problem, such as sticky filmformation, thereby providing a bag having a better film openability,compared with a polyolefin formed by using a Ziegler catalyst liable tohave a larger comonomer content in a lower molecular weight fraction. Itis also known that LLDPE (linear low-density polyethylene) preparedthrough polymerization using a metallocene catalyst (single-sitecatalyst) has a lower density than LLDPE prepared through polymerizationusing a conventional catalyst (multi-site catalyst) at an identicalcomonomer content (e.g., as described in “Plastic” (in Japanese), Vol.44, No. 10, page 81, FIG. 17). There is also known ametallocene-catalyzed LLDPE showing a remarkably lower melting point atan increased comonomer content and at an identical density compared witha Ziegler-catalyzed LLDPE (“PPS Report” (in Japanese), No. 53, October,1994, page 7, FIG. 14). Such metallocene-catalyzed LLDPE is shown tohave a single polymer elusion temperature peak as measured by the ATREF(Analytical Temperature Rising Elution Fractionation) method comparedwith a Ziegler-catalyzed LLDPE showing three polymer elution temperaturepeaks (ibid., page 2, FIG. 1).

The present invention provides a flexible multilayer film excellent informability and sealability based on the characteristics ofmetallocene-catalyzed polyolefin as described above.

The first seal layer constituting the multilayer film of the presentinvention can provide the multilayer film with excellent formability andsealability based on the characteristics of metallocene-catalyzedpolyolefin as described above.

The first seal layer constituting the multilayer film according to thepresent invention may comprise a hermetically sealable resin layersuitable for constituting, e.g., an innermost layer of an inflatedmultilayer film. The second seal layer is a resin layer generallydisposed adjacent to the first seal layer so as to provide a two-layerseal structure together with the first seal layer, thereby takingadvantage of the characteristics of the metallocene-catalyzedpolyolefin. More specifically, the metallocene-catalyzed polyolefinconstituting the first seal layer exhibits excellent sealability, hottack and transparency, but shows insufficient extrudability andfilm-formability, and a single layer thereof cannot readily exhibit asufficient seal strength because of a narrow range of optimum sealingcondition. Thus, the second seal layer should be disposed adjacent tothe first seal layer comprising a metallocene-catalyzed polyolefinalone.

The metallocene-catalyzed polyolefin used in the first seal layer may bean ethylene-based resin, a propylene-based resin or a butene-basedresin. More specifically, the ethylene-based resin may includecopolymers of ethylene in a major proportion (i.e., at least 50 wt. %)and a minor proportion (i.e., at most or less than 50 wt. %) ofα-olefins having up to 10 carbon atoms, such as propylene, butene-1,pentene-1, 4-methyl-pentene-1, hexane-1 and octene-1, including thosegenerally called linear low-density polyethylene (LLDPE), linearmedium-density polyethylene (LMDPE) and very low-density polyethylene(VLDPE). The propylene-based resin and butene-based resin may includehomopolymers of propylene and butene, and copolymers of these monomerswith ethylenes and other α-olefins, such as propylene, butene-1,4-methylpentene-1, hexene-1 and octene-1. A metallocene-catalyzedethylene-based resin (ethylene-based polyolefin) is particularlypreferred because of good sealability, hot tack and transparency.

In order to provide a multilayer film having good film-formability andheat resistance in addition to the sealability, hot tack andtransparency, it is preferred to compose the first seal layer of amixture comprising 90-0 wt. %, more preferably 90-25 wt. %, of ametallocene-catalyzed polyolefin having a crystal melting point of105-145° C., further preferably 105-125° C., and 10-100 wt. %, morepreferably 10-75 wt. %, of a metallocene-catalyzed polyolefin having acrystal melting point of 70-below 105° C., further preferably 86-below105° C. Particularly, the crystal melting point of onemetallocene-catalyzed polyolefin may preferably be at most 100° C. inthe case of a heat-shrinkable film.

In the case of providing a packaging film having good heat-resistanceand good bag openability, it is preferred to use a metallocene-catalyzedpolyolefin having a crystal melting point in the range of from 86° C. tobelow 105° C. A metallocene-catalyzed polyolefin having a crystalmelting point below 86° C. can be used as a portion of themetallocene-catalyzed polyolefin even for such use, but the proportionthereof should preferably be restricted to at most 40 wt. %.

In the case of providing a first seal layer of a mixture resin, thespecies of metallocene-catalyzed polyolefin occupying the largestproportion should have a crystal melting point higher than that of the(principal) resin (component) constituting the second seal layer so asto ensure a good sealability (i.e., bag-making property).

In the case of heat-shrinkable multilayer film, it is preferred that thefirst seal layer contains at least 25 wt. % of a metallocene-catalyzedpolyolefin having a crystal melting point of 105-145° C. so as toprovide further improved resistances to boiling and cooking.

The crystal melting point values referred to herein are based on valuesmeasured as a heat-absorption peak temperature by using a DSC(differential scanning calorimeter) (e.g., “DSC-7”, available fromPerkin-Elmer Corp.).

The metallocene-catalyzed polyolefin constituting the first seal layercan be modified by selective introduction of long-chain branches or canbe blended with a polyolefin produced by polymerization using anothertype of catalyst. Such a polyolefin produced by using another type ofcatalyst should be used only below 50 wt. % so as to retain theexcellent sealability and hot tack of the metallocene-catalyzedpolyolefin. The polyolefin prepared by using another type of catalystmay for example be polyethylene, propylene, copolymers of propylene withother α-olefins, LLDPE, VLDPE or ethylene-vinyl acetate copolymer.

The metallocene-catalyzed polyolefin may preferably have a molecularweight dispersion factor defined as a ratio (Mw/Mn) betweenweight-average molecular weight (Mw) to number-average molecular weight(Mn) of below 3.0, further preferably 1.5-2.8, most preferably 1.9-2.2.The molecular weight dispersion factor may be determined based on theuniversal calibration method based on GPC (gel permeationchromatography) using polystyrene samples having known molecular weightsas calibration standard materials to measure Mw and Mn of a samplemetallocene-catalyzed polyolefin from its GPC chromatogram. By usingsuch a metallocene-catalyzed polyolefin containing little oligomer orlow-molecular weight polymer faction, it is possible to provide amultilayer film with little stickiness.

The second seal layer according to the present invention may preferablycomprise a resin which shows a good adhesiveness to the first seal layerand is provided with improved primary processability, secondaryprocessability and heat-resistance by irradiation with electron rays toprovide a package strength (i.e., seal strength) which is not loweredduring hot sterilization or cold transportation. The second seal layermay comprise a copolymer of ethylene with at least one oxygen-containingmonomer copolymerizable with ethylene having a crystal melting pointlower than that of the (principal) metallocene-catalyzed polyolefin inthe first seal layer, a mixture of such copolymers or a blend of such acopolymer with another polymer. Examples of the copolymer may includecopolymers of ethylene with vinyl acetate, unsaturated acids, such asacrylic acid and methacrylic acid, or C₁-C₄ alkyl esters of suchunsaturated acids, and ionomer resins derived from these copolymers.These copolymers or resins may be used singly or in mixture of two ormore species thereof. In the case of a mixture, the copolymer of thelargest amount thereof should have a crystal melting point lower thanthat of the metallocene-catalyzed polyolefin (of the largest amount) inthe second seal layer.

The copolymer resin constituting the second seal layer may preferablycomprise a copolymer of 80-95 wt. % of ethylene with 20-5 wt. % of atleast one monomer selected from vinyl acetate, acrylic acid, methylacrylate, ethyl acrylate and butyl acrylate, or a blend of thesecopolymers, in view of the stretchability, heat-resistance andcrosslinkability under irradiation with electron rays. The second seallayer can also contain a metallocene-catalyzed polyolefin or anotherethylene-α-olefin copolymer within an extent of not hindering thetransparency of the resultant film.

The crosslinking by electron ray irradiation of the second seal layermay be performed by irradiating a multilayer film including the secondseal layer or irradiating directly the second seal layer beforelamination of the other layers. The irradiation of the multilayer filmmay generally be performed by irradiation through an outermost layerdisposed on the side opposite to the first seal layer. In the case ofproducing the multilayer film by co-extrusion, for example, a moltentubular product (parison) having the first seal layer as the innermostlayer is formed by co-extrusion and is, after or without being quenched,flattened to be irradiated with electron rays. The dose may suitably beon the order of 2-20 Mrad (=20-200 kGY) at an acceleration voltage of150-500 kV. terms of an absorbed dose by the second seal layer.

It is preferred that at least the second seal layer has been crosslinkedby irradiation with electron rays or beam. The other layers may becrosslinked or not crosslinked. In case where the multilayer filmaccording to the present invention includes a gas barrier layer as willbe described hereinafter and the multilayer film including the gasbarrier layer is irradiated with electron rays, if the gas barrier layercomprises a vinylidene chloride copolymer, it is liable to result in anincreased yellowish or brownish tint, but the yellowing can besuppressed by adding glycerin aliphatic acid esters, etc.

The second seal layer may preferably have a thickness larger than,preferably ca. 1.5-ca. 2.5 times, that of the first seal layer in viewof the fact that the metallocene-catalyzed polyolefin principallyconstituting the first seal layer has a low melt tension and in order toeffectively crosslink the second seal layer. On the other hand, thefirst seal layer can be thinned down to a thickness of ca. 3 μm. This isadvantageous for suppressing the cost of the multilayer film while usinga generally expensive metallocene-catalyzed polyolefin. The thickness ofthe first seal layer may be suppressed below a half of the totalmultilayer film thickness and preferably at most 20 μm.

By forming a two-layer seal structure taking advantage of thecharacteristics of metallocene-catalyzed polyolefin, it becomes possibleto provide a flexible multilayer film with improved film-formingcharacteristics, inclusive of primary processabilities, such asextrusion processability, stretch-formability, high-speed bag-makingproperty (sealability) and sealing strength; secondary processabilities,such as deep drawability and skin-packaging characteristic; and otherimproved packaging film performances, such as heat-shrinkability forpreventing the occurrence of meat-juice within or out of food packageproducts, boiling resistance for thermal sterilization and cookingresistance for cooking.

The outermost layer may be disposed on an opposite side of the firstseal layer with respect to the second seal layer. It is important forthe outermost layer to exhibit an anti-sticking property to a sealingbar used for the sealing so as to be suitably used in an automaticpackaging machine or a high-speed bag-making machine including acontinuous sealing operation. In the multilayer film according to thepresent invention, it is preferred that the outermost layer does notcontain an ionomer resin,a metallocene-catalyzed polyolefin, or apropylene-ethylene random copolymer of little crystal orientationcharacteristic in stretching. A flexible multilayer film excellent incontinuous sealability may be obtained by using the outermost layercomprising a thermoplastic resin, inclusive of polyester resins,polyamide resins or ethylene-based resins, such as α-olefin resinsobtained by using a Ziegler catalyst, linear low-density polyethylene(LLDPE), linear medium-density polyethylene (LMDPE), very low-densitypolyethylene (VLDPE), and copolymers of ethylene with vinyl acetate,unsaturated acids, such as acrylic acid and methacrylic acid, or alkylesters of such unsaturated acids.

The multilayer film according to the present invention can include atleast one intermediate layer functioning as a gas barrier layer inaddition to the first seal layer and the second seal layer. The gasbarrier resin may comprise a resin selected from, e.g., vinylidenechloride copolymers, ethylene-vinyl alcohol copolymer, aromatic nylonsinclusive of polyamide formed by polycondensation betweenmethaxylyenediamine and adipic acid, and polyamide formed fromterephthalic acid and/or isophthalic acid and hexamethylenediamine,amorphous nylon, semi-crystalline nylon, and acrylonitrile-basedcopolymers. It is also possible to use a polymer blend, inclusive of: amixture resin composition comprising principally a vinylidene chloridecopolymer, and a copolymer of ethylene with vinyl acetate, anunsaturated acid, such as acrylic acid or methacrylic acid, or an alkylester thereof, or an MBS (methyl methacrylate-butadiene-styrenecopolymer) resin; a mixture resin composition comprising principallyethylene-vinyl alcohol copolymer having a saponification degree of atleast 95 mol. %, and polyester elastomer, polyamide elastomer,ethylene-vinyl acetate copolymer, ethylene-acrylate ester copolymer, orethylene-vinyl alcohol copolymer having a saponification degree of below95 mol. %; and a mixture resin composition comprising theabove-mentioned aromatic nylon and an aliphatic nylon. It is generallymost preferred to use a vinylidene chloride-based copolymer, whileethylene-vinyl alcohol copolymer may be preferred in the case requiringa particularly good flexibility.

Herein, the vinylidene chloride copolymers may include copolymers ofvinylidene chloride and at least one mono-ethylenically unsaturatedmonomer copolymerizable with vinylidene chloride. The mono-ethylenicallyunsaturated monomer may be used in a proportion of 2-40 wt. %,preferably 4-35 wt. %, of the resultant vinylidene fluoride copolymer.Examples of the mono-ethylenically unsaturated monomer may include vinylchloride, vinyl acetate, vinyl propionate, alkyl acrylates, alkylmethacrylates, acrylic acid, methacrylic acid, itaconic acid,acrylonitrile, acrylamide, vinyl alkyl ethers, vinyl alkyl ketones,acrolein, allyl esters and ethers, butadiene, and chloroprene. Thevinylidene chloride copolymer can also be a ternary or quarternarycopolymer. It is particularly preferred to use a copolymer with vinylchloride or a C₁-C₈ alkyl (meth)acrylate, such as methyl acrylate, ethylacrylate or methyl methacrylate.

The gas barrier layer may have a thickness appropriately selecteddepending on the desired level of gas barrier property of the resultantpackaging material. In the case of forming a gas barrier layercomprising a vinylidene chloride copolymer by co-extrusion, thethickness of the layer may preferably be at most 30% of the total filmthickness in view of the thermal stability and low-temperatureresistance of the multilayer film.

An adhesive layer may be disposed between the respective layers in casewhere a sufficient adhesion is not ensured between adjacent layers. Theadhesive resin may preferably comprise a thermoplastic polymer,copolymer or terpolymer, a modification product of such a thermoplasticresin with an unsaturated carboxylic acid, a modification product ofsuch an acid-modified product further with a metal, or a blend of theabove. Specific examples thereof may include: ethylene-vinyl acetatecopolymer, ethylene-ethyl acrylate copolymer, olefin copolymers modifiedwith maleic acid, itaconic acid, or an anhydride thereof, athermoplastic polyurethane elastomer, and a blend of these resins. Theadhesive layer may preferably have a thickness of at most 5 μm, morepreferably 1-3 μm. It is particularly preferred to suppress thethickness of an adhesive of, e.g., an anhydride-modified resin, such asone modified with maleic anhydride, in view of a weak cohesion andexpensiveness of the modified resin.

The multilayer film can further include an additional resin layercomprising, e.g., a polyamide resin or a thermoplastic polyester resin.By including such an additional resin layer, the multilayer filmaccording to the present invention may be provided with further improvedbag-making characteristic and heat resistance in combination with theabove-mentioned two-layer structure. In order to obtain a flexiblemultilayer film, it is appropriate to dispose such a layer of polyamideresin or thermoplastic polyester resin as an intermediate layer. On theother hand, if the resin layer is disposed as the outermost layer, thethickness thereof may preferably be suppressed to 0.5-3 μm. If theoutermost layer has too large a thickness, the layer is liable to bepealed at a boundary with an inner layer, such as a gas barrier layer.In order to provide a satisfactory film-formability in combination, themultilayer film as a whole may preferably have a secant modulus at 2.5%strain in the range of 150-450 MPa even in case where the total filmthickness is 30 μm or larger.

The polyamide resin used for the above purpose may be at least onespecies of aliphatic nylon selected from, e.g., nylon 6, nylon 11, nylon12, nylon 66, nylon 69, nylon 610, nylon 612, and copolymer nylonsincluding nylon 6-9, nylon 6-10, nylon 6-12, nylon 66-66, nylon 66-69,and nylon 66-66-610; an aromatic nylon, such as one formed fromhexamethylenediamine and an aromatic dibasic acid; or a semi-crystallineor amorphous nylon.

Preferred examples of the thermoplastic polyester resin may includethose obtained from an acid component comprising an aromatic dibasicacid, such as terephthalic acid or isophthalic acid, and a glycolcomponent comprising an aliphatic glycol, an alicyclic glycol or anaromatic glycol, such as ethylene glycol, diethylene glycol orcyclohexane dimethanol. For the multilayer film according to the presentinvention, it is preferred to use a co-polyester formed by using two orthree species of acid component or/and glycol component.

The polyamide resin or thermoplastic polyester resin can be blended withanother resin, such as thermoplastic polyurethane resin, as desired. Inthe case of co-extrusion with a vinylidene chloride co-polymer for a gasbarrier layer, the polyamide resin or thermoplastic polyester resin maypreferably have a crystal melting point, if any, of at most 200° C.

The respective resin layers of the multilayer film according to thepresent invention can contain an optional additive, such as a processingaid, a surfactant (for preventing for, for imparting anti-cloudingproperty, slippability, etc.), or an anti-static agent, within an extentof not adversely affecting the purpose of the present invention.Further, for the purpose of providing an improved met-adhesion with foodproduct, such as processed meat, it is possible to apply a coronadischarge treatment to the first seal layer side or the opposite side ofthe multilayer film.

For a recycle purpose, it is possible to incorporate a pulverizate ofthe multilayer film containing a metallocene-catalyzed polyolefin intothe respective component layers of the multilayer film or include anadditional layer of the pulverizate in the multilayer film according tothe present invention within an extent of not adversely affecting theperformances of the multilayer film. The pulverizate may be ordinarilyincorporated into an intermediate layer other than the first seal layerand the outermost layer. As the metallocene-catalyzed polyolefin has alow melt tension, the blend thereof with a gas barrier layer resin, suchas vinylidene chloride co-polymer or ethylene-vinyl alcohol co-polymer,may provide an improved fluidity in an extruder or a die mold tofacilitate the provision of a uniform film thickness. In the case ofblending the pulverizate with the gas barrier layer resin, the blendingratio may be suppressed to at most ca. 10 wt. %, preferably at most ca.10 wt. %, while depending on the required level of gas barrier propertyand transparency of the resultant film. Further, the gas barrier layerof, e.g., a vinylidene chloride co-polymer can contain a pulverizate ofanother vinylidene chloride co-polymer film or in lamination withanother layer of such a pulverizate.

The multilayer film according to the present invention may generally beformed through co-extrusion but can also be formed through extrusioncoating or lamination, or a combination of these. The multilayer filmaccording to the present invention can be coated with a vapor-depositedlayer of aluminum, silica, etc., or laminated with another filmincluding such a vapor-deposition layer, to form a new type of packagingmaterial.

The multilayer film according to the present invention having aheat-shrinkability through stretch-orientation may for example beprepared by the coextrusion-inflation method or the T-die stretchingmethod to provide a suitable food-packaging material. The shrinkabilitycan vary depending on the usage, but may for example be at least ca. 30%in both longitudinal and transverse directions at, e.g., 70° C. forlow-temperature shrinkage for fresh meat packaging; ca. 25-ca. 50%,e.g., at 90-95° C. for hot sterilization for processed meat packaging;or ca. 35-ca. 50%, e.g., at 100° C., for tray packaging. The multilayerfilm for such usages may preferably have a total thickness of 10-120 μm.

Some typical laminar structures from the first seal layer side to theoutermost layer of the multilayer film according to the presentinvention are as follows.

(1) Surface layer (first seal layer)/second seal layer/gas barrierlayer/surface layer,

(2) Surface layer (first seal layer)/second seal layer/gas barrierlayer/intermediate layer/surface layer,

(3) Surface layer (first seal layer)/second seal layer/intermediatelayer/surface layer.

An adhesive layer may be disposed between any pair of adjacent layersdescribed above.

As described above, in order to have a satisfactory film-formability,the multilayer film according to the present invention may preferablyhave a secant modulus at 2.5% strain (a tensile secant modulus asmeasured according to JIS K7127) in the range of 150-450 MPa. In thecase of a film having a thickness of 30 μm or larger, the secant modulusmay preferably be 150-400 MPa. The good film-formability herein refersto properties of allowing a stable extrudability and a stablestretchability without trouble, thereby providing a film of a uniformthickness. A uniform film thickness leads to a highspeed bag-makingperformance. The 2.5%-strain secant modulus in the range of 150-450 MPamay readily provide these performances and also mean that the film isnot too flexible or too rigid, exhibit good packaging performance on thematerial to be packed and shows good adaptability to an automaticpackaging machine.

The present invention will be described more specifically based onExamples and Comparative Examples hereineblow.

In Examples and Comparative Examples shown below, the following resinssometimes denoted by their abbreviative symbols were used, includingmetallocene-catalyzed ethylene-α-olefin co-polymers all showing amolecular weight distribution factor of below 3. The melt-index (MI)values (in the unit of “g/10 min.”) were obtained at 190° C. under aload of 2.1 kg. Part(s) means “part(s) by weight”.

(1) MePE-1: metallocene-catalyzed ethylene-hexene-1 co-polymer (“Exact9017”, mfd. by Exxon Co.; crystal melting point (MP)=112° C., MI=3.0,density (d)=0.920 (g/cm³)).

(2) MePE-2: metallocene-catalyzed ethylene-octene-1 co-polymer(“Affinity FM1570” (formed by using a constrained geometry catalyst),mfd. by Dow Chemical Co.; MP=108° C., MI=1.0, d=0.915; Mw/Mn=1.9-2.2).

(3) MePE-3: metallocene-catalyzed ethylene-octene-1 co-polymer(“Affinity PL1880” (formed by using a constrained geometry catalyst),MP=100° C., MI=1.0, d=0.902, Mw/Mn=1.9-2.2).

(4) MePE-4: metallocene-catalyzed ethylene-butene-1 co-polymer (“Exact3010C”, mfd. by Exxon Co.; MP=87° C., MI=3.5, d=0.900).

(5) MePE-5: metallocene-catalyzed ethylene-butene-1 co-polymer (“Exact4011”, mfd. by Exxon Co.; MP=78° C., MI=2.2, d=0.885).

(6) EVA-1: ethylene-vinyl acetate co-polymer (vinyl acetate (VA)content=6 wt. %, MP=96° C., MI=3.3).

(7) EVA-2: ethylene-vinyl acetate co-polymer (VA content=10 wt. %,MP=91° C., MI=1.5).

(8) EVA-3: ethylene-vinyl acetate co-polymer (VA content=15 wt. %,MP=84° C., MI=1.5).

(9) EVA-4: ethylene-vinyl acetate co-polymer (VA content=15 wt. %,MP=82° C., MI=4.2).

(10) EVA-5: ethylene-vinyl acetate co-polymer (VA content=25 wt. %,MP=70° C., MI=2).

(11) M-EVA: carboxylic acid-modified ethylene-vinyl acetate-acrylic acidco-polymer.

(12) EEA-1: ethylene-ethyl acrylate co-polymer (ethyl acrylate (EA)content=7 wt. %, MP=97° C., MI=1.5).

(13) EEA-2: ethylene-ethyl acrylate co-polymer (EA content=15 wt. %,MP=85° C., MI=1.5).

(14) VLDPE: ethylene-butene-1 co-polymer (d=0.902, MP=115° C., MI=2.0).

(15) VLDPE: ethylene-4-methylpentene-1 co-polymer (d=0.922, MP=120° C.,MI=2.1).

(16) PP: propylene-ethylene random co-polymer (ethylene content=7 wt. %,MP=137° C.).

(17) IO: ionomer (Na-type; MP=87° C.).

(18) PVDC-1: vinylidene chloride (VDC) co-polymer (VDC/vinyl chloride(VC)=82/18 (by weight)) containing 5 wt. parts each of a stabilizer anda plasticizer per 100 wt. parts of the VDC co-polymer:

(19) PVDC-2: vinylidene chloride (VDC) co-polymer (VDC/VC=88/12 (byweight)) containing 3 wt. parts of ethylene-vinyl acetate co-polymer (VAcontent=28 wt. %) and 5 wt. parts each of a stabilizer and a plasticizerper 100 wt. parts of the VDC co-polymer. (20) EVOH-1: ethylene-vinylalcohol co-polymer (ethylene content=44 mol. %, saponificationdegree=99%).

(21) EVOH-2: mixture of 100 wt. parts of EVOH-1 and 3 wt. parts ofethylene-vinyl acetate co-polymer.

(22) NY-1: nylon 6-66 co-polymer (MP=195° C.).

(23) NY-2: nylon 6-12 co-polymer (MP=120° C.).

(22) PET-1: polyethylene terephthalate (95 mol. % of terephthalic acidand 5 mol. % of isophthalic acid: MP=237° C.).

(23) PET-2: polyethylene terephthalate (90 mol. % of terephthalic acidand 10 mol. % of isophthalic acid: MP=225° C.).

(26) A-NY: polycondensate of hexamethylenediamine with terephthalic acidand isophthalic acid (“Sealer PA 3426”, mfd. by Mitsui Dupont K.K.;d=1.18, no crystal melting point).

EXAMPLES 1-2 Comparative Example 1

Six-layered laminate products each having a layer structure as shown inTable 1—1 appearing hereinafter were produced by co-extrusion so thatthe first seal layer (1st layer) constituted the innermost layer. Eachextruded tubular molten product (parison) was irradiated from theoutermost layer thereof with electron rays at a dose of 10 Mrad and anacceleration voltage of 400 kV and, after reheating, subjected toinflation at stretching ratios of 3.2 times in a longitudinal directionand 3 times in a transverse direction to form a multilayer film havingindividual layer thicknesses sequentially from the 1st layer of10/20/1/8/1/18 (μm) and a lay flat width of ca. 400 mm. The films ofExamples 1-2 showed 2.5%-secant moduli (JIS K7127) of 150-180 MPa inboth longitudinal and transverse directions and heat-shrinkabilities of38-43% (at 70° C.) in both longitudinal and transverse directions asmeasured with respect to a square sample of 10 cm (length)×10 cm (width)after dipping for 5 sec in a bath of water at the indicated temperature.

During the above-mentioned film formation, each film composition wasevaluated with respect to the film-formabilities.

Each type of the resultant multilayer films was then supplied to abag-making machine (Model “HBM”, mfd. by Toyama Sanki K.K.) to formseveral circularly bottom-sealed bags. The bags were then packed withfresh meat and evaluated with respect to the bag openability forpacking, the adhesion between the meat and the film afterheat-shrinkage, the leakage at the seal lines, the occurrence ofmeat-juice, and the rupture of the bag after dropping.

The results of the evaluation are summarized in Table 1-2 according tothe evaluation standards shown below the table.

TABLE 1-1 Layer structure^(*1) 1st 2nd 3rd 4th 5th 6th Ex. 1 MePE-4EVA-3 EVA-4 PVDC-1 EVA-4 EVA-3 95% EVA-2 5% Ex. 2 MePE-4 EVA-3 EVA-4PVDC-1 EVA-4 EVA-3 60% 95% MePE-5 EVA-2 40% 5% Comp. MePE-4 EVA-2 EVA-4PVDC-1 EVA-4 MePE-4 Ex. 1 ^(*1)“%” in the table represents wt. % of thecomponent in each layer.

TABLE 1-2 Film properties Ex. 1 Ex. 2 Comp.Ex. 1 Extrudability A A BStretchability A A B⁻ Bag formability (1) A A B Fresh meatpackageability A A B⁻

(Extrudability)

A: Easily formed into a parison without entanglement of resin below theextrusion die.

B: Liable to cause entanglement so that the parison formation wassomewhat difficult.

(Stretchability (Inflation Stability))

A: Stable inflation was possible without substantial vibration of theshoulder.

B: Inflation was unstable due to a remarkable vibration of the shoulder,so that the sample could be formed in a length of only several hundredmeters.

(Bag-formability (1))

Evaluated by using a bag-manufacturing machine for providing a circularbottom-sealed bags (“Model HBM”, available from Toyama Sanki K.K.).

A: A good bag-making rate of 70 bags/min.

B: Liable to cause sticking of the film onto the seal bar, thusresulting in a smaller seal thickness. The bag-making rate was 30bags/min.

(Fresh Meat Packaging Performance)

A: The film closely fitted to the fresh meat (ca. 8 kg) at aheat-shrinkage temperature of 77° C., and the resultant packed bag didnot cause a rupture at the seal line by dropping from a height of 1 m.

A⁻: Exhibited a good heat-shrinkability at 77° C. and a good result atthe 1 m-dropping test. The bag openability for packaging was not sogood. Good adhesion was exhibited between films, and no noticeabledripping was observed.

B⁻: The bags were ruptured at a rate of one from three at the 1m-dropping test.

EXAMPLES 3-5 Comparative Examples 2-3

Six-layered laminate products each having a layer structure as shown inTable 2-1 were produced by co-extrusion so that the first seal layer(1st layer) constituted the innermost layer. Each extruded parison wasirradiated from the outermost layer side with electron rays at a dose of12 Mrad and an acceleration voltage of 300 kV and, after reheating,subjected to inflation at stretching ratio of 2.8 times in alongitudinal direction and 2.5 times in a transverse direction to form amultilayer film having individual layer thicknesses sequentially fromthe 1st layer of 12/18/1/8/1/14 (μm) and a lay flat width of ca. 400 mm.The films of Examples 3-5 showed 2.5%-secant moduli of 200-220 MPa inboth longitudinal and transverse directions and heat-shrinkabilities (at90° C.) of 45-50% in both longitudinal and transverse directions. Themultilayer film of Comparative Example 2 was poor in gloss.

Each type of the multilayer films was then supplied to a bag-makingmachine (“Model DSWH”, available from Taiyo Shokai K.K.) to form severalside-sealed bags. The bags were then packed with processed meat,subjected to 10 min. of hot sterilization at 95° C., and then evaluatedwith respect to the adhesion between the meat and bag, the rupture atthe seal line and the occurrence of dripping. The results are summarizedin Table 2—2.

TABLE 2-1 1st 2nd 3rd 4th 5th 6th Ex. 3 MePE-2 EVA-2 EEA-2 PVDC-1 EEA-2VLDPE 99% 80% MePE-3 EVA-3 10% 20% Ex. 4 MePE-1 EVA-2 EVA-4 PVDC-1 EVA-4EVA-1 25% 80% MePE-3 LLDPE 75% 20% Ex. 5 MePE-2 EEA-1 EEA-2 PVDC-1 EEA-2VLDPE 50% MePE-4 10% VLDPE 40% Comp. MePE-1 MePE-4 EVA-4 PVDC-2 EVA-4MePE-4 Ex. 2 30% MePE-4 70% Comp. EVA-1 MePE-3 EVA-4 PVDC-1 EVA-4 VLDPEEx. 3

TABLE 2-2 Comp. Comp. Ex.3 Ex.4 Ex.5 Ex.2 Ex.3 Extrudability A A A B⁻ AStretchability A A A B⁻ B⁻ Bag formability A A A C B⁻ (2) Processed meatA A A — C packageability

(Extrudability)

Same as in Table 1-1

B⁻: Liable to cause entanglement of the resin below the extrusion die sothat the parison formation was very difficult.

(Stretchability)

Same as in Table 1-1.

(Bag-formability (2))

Evaluated by using a bag-manufacturing machine for providing side-sealedbags (“Model DSWH”, mfd. by Taiyo Shokai K.K.).

A: A good bag-making rate of 80 bags/min.

B⁻: Some bags caused a melt-cutting at the seal line because of filmthickness irregularity (caused by instability of inflation bubbleshoulder). The bagmaking rate was 30 bags/min.

C: Generally caused a melt-sticking at the seal line because of the filmthickness irregularity (caused by instability of inflation bubbleshoulder) and the sticking onto the seal bar.

(Processed meat packageability)

A: Good cling at a hot-sterilization temperature of 95° C. No dripping(meat-juice) was noticed. Exhibited good boiling resistance causing nobreakage at the seal line.

C: Caused a breakage of bag from the seal line at a hot sterilizationtemperature of 95° C.

−: Not measured.

EXAMPLES 6-7, Comparative Examples 4-5

Eight-layered laminate products each having a layer structure as shownin Table 3-1 were produced by co-extrusion so that the first seal layer(1st layer) constituted the innermost layer. Each extruded parison wasirradiated from the outermost layer side with electron rays at a dose of8 Mrad and an acceleration voltage of 350 kV and, after reheating,subjected to inflation at stretching ratios of 3.2 times in alongitudinal direction and 3.0 times in a transverse direction to form amultilayer film having a lay flat width of ca. 350 mm and havingindividual layer thicknesses sequentially from the 1st layer of8/20/2/10/2/10/2/4 (μm) (Examples 6, 7 and Comparative Example 4) and18/10/2/10/2/10/2/4 (μm) (Comparative Example 5). The films of Examples6-7 showed 2.5 %-secant moduli of 220-240 MPa in both longitudinal andtransverse directions and heat-shrinkabilities (at 85° C.) of 40-45% inboth longitudinal and transverse directions. The multilayer film ofExample 7 showed a slightly pearl-like appearance.

Each type of the multilayer films was then supplied to a bag-makingmachine (“Model HBM”, available from Toyama Sanki K.K.) to form severalcircular bottom-sealed bags similarly as in Example 1. The bags werethen packed with pork meat, and evaluated with respect to the bagopenability for packing, the adhesion between the meat and the filmafter heat-shrinkage, the leakage from the seal lines, the occurrence ofdripping, and the rupture of the bag after dropping.

The results are summarized in Table 3-2.

TABLE 3-1^(*1) 1st 3rd 4th 5th 6th 7th 8th Ex. 6 MePE-3 M-EVAPVDC-2^(*2) M-EVA NY-2 M-EVA EVA-1 Ex. 7 MePE-3 EVA-4 PVDC-2^(*3) EVA-4IO EVA-4 VLDPE Comp. VLDPE M-EVA PVDC-2 M-EVA NY-2 M-EVA VLDPE Ex. 4Comp. MePE-3 M-EVA PVDC-2 M-EVA NY-2 M-EVA VLDPE Ex. 5^(*4) ^(*1)Thesecond layer in each Example comprised EVA-2. ^(*2)PVDC-2 (for Ex. 6)contained 30 wt. % of pulverizate of a single layer film of PVDC-2.^(*3)PVDC-3 (for Ex. 7) contained 5 wt. % of pulverizate of the parisonof Example 7. ^(*4)The multilayer film of Comparative Example 5 hadsuccessive layer thicknesses of 18/10/2/10/2/10/2/4 (μm).

TABLE 3-2 Ex.6 Ex.7 Comp.Ex.2 Comp.Ex.3 Extrudability A A A B⁻Stretchability A A A B⁻ Bag formability A A B B⁻ (1) Pork meat A A C —packageability

(Extrudability)

Same as in Table 1-1

B⁻: Liable to cause entanglement of the resin below the extrusion die sothat the parison formation was very difficult.

(Stretchability)

Same as in Table 1-1.

B⁻: Inflation was unstable because of remarkable vertical vibration ofthe shoulder, so that the sample could be formed in a length of onlyseveral hundred meters. No improvement was given by increasing theheating temperature for stretching.

(Bag-formability (1))

Similarly as in Table 1-2.

A: A good bag-making rate of 80 bags/min.

B⁻: To facilitate the bag opening, air was blow thereinto, but the sealline was liable to be wrinkled. The bag-making rate was 30 bags/min.

(Pork Meat Packageability)

A: The film closely fitted to the pork meat (ca. 6 kg) at a heatshrinkage temperature of 90° C., and the resultant packaged bag did notcause a rupture by dropping from a height of 1 m.

C: The bag openability for packing was not good. Some leakage wasobserved at the wrinkled seal line by checking with a redalcohol-containing penetrating liquid.

EXAMPLE 8 Comparative Example 6

Seven-layered laminate products each having a layer structure as shownin Table 4-1 were produced by co-extrusion so that the first seal layer(1st layer) constituted the innermost layer. Each extruded parison wasirradiated from the outermost layer side (7th layer) with electron raysat a dose of 4 Mrad and an accelerating voltage of 200 kV and, afterreheating, subjected to inflation at stretching ratio of 2.6 times in alongitudinal direction and 2.5 times in a transverse direction to form amultilayer film having individual layer thicknesses sequentially fromthe 1st layer of 10/11/1.5/5/11/1.5/4 (μm) and a lay flat width of ca.450 mm. The films of Example 8 and Comparative Example 6 showed2.5%-secant moduli of 370-390 MPa in both longitudinal and transversedirections and heat-shrinkabilities (at 90° C.) of 40-45% in bothlongitudinal and transverse directions.

Each type of the multilayer films was supplied to a pillow-packagingmachine (“NW Pillow-Packaging Machine”, mfd. by Ohmori Kikai K.K.) toform three-side-sealed processed meat packages. The resultant processedmeat packages were subjected to 10 min. of hot sterilization at 95° C.and evaluated with respect to the adhesion between the meat and film,the rupture at the seal line and the occurrence of meat-juice. Theresults are summarized in Table 4-2.

TABLE 4-1 1st 2nd 3rd 4th 5th 6th 7th Ex. 8 MePE-2 EVA-2 M-EVA EVOH-1NY-1 M-EVA EVA-1 90% 70% MePE-3 NY-2 10% 30% Ex. 9 VLDPE EVA-2 M-EVAEVOH-2 NY-1 M-EVA PP 70% NY-2 30%

TABLE 4-2 Ex. 8 Comp.Ex.6 Extrudability A A Stretchability A APackageability A C Processed meat A C packageability

(Extrudability), (Stretchability)

Same as in Table 1-2.

(Packageability (or Sealability))

A: A good packaging rate of 18 m/min.

C: The multilayer film stuck to a rotating rear seal bar so that thepackaging was interrupted several times. The seal part thickness wasalso reduced. An increased amount of starch powder was applied in orderto prevent film blocking, so that the refuse thereof attached to theseal line, thus failing to provide a fine seal line.

(Processed Meat Packageability)

A: Exhibit a good boiling resistance such that the packaged processedmeat (of ca. 200 g) did not cause a rupture at the seal line even afterhot sterilization at 95° C.. The film showed a good adhesion, and nomeat-juice was noticed.

C: Leakage was observed at the three-side seal line after hotsterilization at 95° C. as a result of checking with a redalcohol-containing penetrating liquid.

EXAMPLES 9-10

Seven- or six-layered laminate products each having a layer structure asshown in Table 5-1 were produced by co-extrusion so that the first seallayer (1st layer) constituted the innermost layer. Each extruded parisonwas, after reheating, subjected to inflation at stretching ratio of 3times in a longitudinal direction and 3 times in a transverse directionand then longitudinally slit into two sheets of multilayer film eachhaving a width of ca. 390 mm and individual layer thicknessessequentially from the first layer of 3/7/1/2.5/4.5/1/1 (μm) (Example 9)and 4/9/1/4/1/1 (μm) (Example 10). The films of Examples 9-10 showed2.5%-secant moduli of 40-45 MPa in both longitudinal and transversedirections and heat-shrinkabilities (at 100° C.) of 43-47% in bothlongitudinal and transverse directions.

Each multilayer film was supplied to a packaging machine (“Model FW,mfd. by Fuji Kikai K.K.) to form three side-sealed packages eachcontaining a sliced ham-loaded tray. The packages were then passedthrough an oven at a temperature of 110° C. and thereafter observed withrespect to the film adhesion state and the occurrence of leakage at theseal line. The results are shown in Table 5-2.

TABLE 5-1 1st 2nd 3rd 4th 5th 6th 7th Ex. 9 MePE-2 EVA-2 M-EVA EVOH-1NY-1 M-EVA PET-2 90% 80% MePE-3 A-NY 10% 20% Ex. 10 MePE-2 EVA-2 M-EVANY-1 M-EVA PET-2 90% 60% MePE-3 NY-2 10% 40%

TABLE 5-2 Ex. 9 Ex. 10 Extrudability A A Stretchability A APackageability A A Tray packageability A A

(Extrudability) (Stretchability)

Same as in Table 1-2.

(Packageability—Sealability)

A: A good packaging rate of 80 packages/min.

(Tray packageability)

A: The packaging film tightly fitted onto the sliced ham on the trayafter passing through the oven at 110° C.. No leakage was observed as aresult of checking with a red alcohol-containing penetrating liquid.

EXAMPLES 11-12 Comparative Example 7

Four- or six-layered laminate products each having a layer structure asshown in Table 6-1 were produced by co-extrusion so that the first seallayer (1st layer) constituted the innermost layer. Each parisonimmediately after passing through the extrusion die was subjected toinflation and then slit into two sheets of multilayer film each having awidth of ca. 405 mm and individual layer thicknesses sequentially fromthe 1st layer of 15/30/2/2 (μm) (Example 11), 12/30/1/5/1/1 (μm)(Example 12) and 15/30/2/2 (μm) (Comparative Example 7). The films ofExamples 11-12 showed 2.5%-secant moduli of 300-350 MPa in bothlongitudinal and transverse directions and no heat-shrinkability in anyof longitudinal and transverse directions as measured at 90° C. for 5sec.

Each multilayer film was supplied to a pillow-packaging machine (“NWPillow-Packaging Machine”, mfd. by Ohmori Kikai K.K.) to formthree-side-sealed processed meat packages. The resultant processed meatpackages were subjected to 10 min. of hot sterilization at 95° C. andevaluated with respect to the cling between the meat and film, therupture at the seal line and the occurrence of meat-juice. The resultsare summarized in Table 6-2.

TABLE 6-1 1st 2nd 3rd 4th 5th 6th Ex. 11 MePE-1 EVA-2 M-EVA PET-1 90%MePE-4 10% Ex. 12 MePE-1 EVA-2 M-EVA EVOH-1 M-EVA PET-2 90% MePE-4 10%Comp. MePE-1 MePE-4 M-EVA PET-1 Ex. 7

TABLE 6-2 Ex. 11 Ex. 12 Comp.Ex.7 Extrudability A A C Stretchability A AC Packageability A A — Processed meat A A — packageability

(Extrudability)

Same as in Table 1-2

C: The parison formation was impossible because of entanglement belowthe extrusion die.

(Stretchability)

A: The inflation was performed with stable shoulder formation by using acooling mantle.

C: The shoulder could not be formed.

(Packageability (or sealability))

A: A good packaging rate of 18 m/min.

(Processed meat packageability)

Same as in Table 4-2.

As is understood from the above-mentioned Examples and ComparativeExamples, the multilayer film having the two-layer seal structureincluding the specified first seal layer and second seal layer accordingto the present invention has provided an improvement to the filmformability which has been a weak point of metallocene-catalyzedpolyolefin and provided improved properties including primaryprocessabilities, such as extrudability, stretchability, high-speedbag-formability (sealability), and strength; secondary processabilities,such as deep drawing characteristic and skin packaging characteristic;and further heat-shrinkability for preventing the occurrence ofmeat-juice within or out of food packages, boiling resistance desirablefor hot sterilization and cooking resistance desirable for cooking.

What is claimed is:
 1. A plastic container comprising a multilayer film,including: a first seal layer comprising principally ametallocene-catalyzed polyolefin, and a second seal layer comprising aco-polymer of at least one oxygen-containing monomer and ethylene, saidsecond seal layer being disposed adjacent to said first seal layer; saidco-polymer having a crystal melting point lower than that of themetallocene-catalyzed polyolefin, wherein the first seal layer isdisposed as an innermost layer, and mutually opposite edges of the firstseal layer are sealed to each other to form the container.
 2. Theplastic container according to claim 1, wherein the second seal layerhas a thickness larger than that of the first seal layer.
 3. The plasticcontainer according to claim 1, wherein the first seal layer comprises amixture of at least 50 wt. % of the metallocene-catalyzed polyolefin andanother metallocene-catalyzed polyolefin, and the second seal layercomprises a mixture of a largest amount of the co-polymer and a smalleramount of another resin.
 4. The plastic container according to claim 1,wherein the multilayer film has a secant modulus at 2.5% strain of150-450 MPa.
 5. The plastic container according to claim 1, wherein thesecond seal layer has been crosslinked by irradiation with electronrays.
 6. The plastic container according to claim 1, wherein saidmetallocene-catalyzed polyolefin is an ethylene-based resin.
 7. Theplastic container according to claim 1, wherein saidmetallocene-catalyzed polyolefin has a weight-average molecular weight(Mw)/number-average molecular weight (Mn) ratio below
 3. 8. The plasticcontainer according to claim 1, wherein said metallocene-catalyzedpolyolefin is a mixture of a metallocene-catalyzed polyolefin having acrystal melting point of 105-145° C. and a metallocene-catalyzedpolyolefin having a crystal melting point of 70° C. to below 105° C. 9.The plastic container according to claim 1, wherein said second seallayer comprises a co-polymer of 80-95 wt. % of ethylene and up to 20 wt.% of at least one monomer selected from the group consisting of vinylacetate, acrylic acid, methyl acrylate, ethyl acrylate and butylacrylate.
 10. The plastic container according to claim 1, comprising atleast three layers further including an outermost layer of athermoplastic resin disposed on an opposite side of the first seal layerwith respect to the second seal layer.
 11. The plastic containeraccording to claim 1, wherein the multilayer film further includes a gasbarrier layer.
 12. The plastic container according to claim 1, whereinthe multilayer film has heat-shrinkability.
 13. The plastic containeraccording to claim 1, wherein the multilayer film comprises an as-blowntubular film and is bottom-sealed to provide the container.
 14. Theplastic container according to claim 1, wherein the multilayer film issealed at plural sides thereof to form the container.
 15. A packagedproduct, comprising a plastic container comprising a multilayer film,including: a first seal layer comprising principally ametallocene-catalyzed polyolefin, and a second seal layer comprising aco-polymer of at least one oxygen-containing monomer and ethylene; saidco-polymer having a crystal melting point lower than that of themetallocene-catalyzed polyolefin, wherein the first seal layer isdisposed as an innermost layer, and a content material is packed withinthe container by sealing mutually opposite edges of the first seal layerto each other.